The invention relates to an oscillator, comprising a resonator which includes at least one capacitor and at least one inductor, said resonator being designed to supply a first signal of a first frequency at an output of the resonator; and a frequency multiplier or frequency divider having an input which is connected directly or indirectly to the resonator output, said frequency multiplier or frequency divider, respectively, being designed to supply a second signal of a second frequency at an output of the frequency multiplier or frequency divider, respectively, the second frequency being n times or 1/n times, respectively, (nxe2x89xa72 and integer) the first frequency. The invention further relates to a transmitter which is provided with such an oscillator, and the use of such a transmitter for various applications.
When oscillators are used, electromagnetic feedback between the oscillator output signal (the second signal) and the resonator circuit may result in the frequency of the oscillator output signal deviating considerably from the set frequency, which is highly undesirable. Such feedback can arise, for example, via the supply voltage, as a result of the component configuration chosen, via an amplifier circuit or, if the oscillator forms part of a transmitter or a transceiver, via the electromagnetic radiation emitted by an antenna.
One measure taken in the prior art to reduce electromagnetic feedback in an oscillator is to employ a frequency doubler downstream of the resonant circuit. Feedback of the frequency-doubled signal to the resonant circuit leads to said signal being filtered out by the resonant circuit. In the ideal case, therefore, no frequency deviation due to electromagnetic feedback will occur. In practice, however, frequency mixing products being generated in the oscillator do give rise to frequency deviations as a result of non-linearities in the oscillator circuits which cause the frequency products of signals to be generated.
It is an object of the invention to further suppress frequency deviation in an oscillator output signal resulting from electromagnetic feedback when a frequency multiplier or a frequency divider is used.
To this end, the oscillator according to the invention is characterized by a tuned circuit which is part of the resonator and which forms a short circuit or an open connection for the second frequency. Thanks to this measure it is possible, notwithstanding the nonlinearity of oscillator components, to largely suppress oscillator frequency deviation resulting from electromagnetic feedback.
In a preferred embodiment, the resonator comprises a series connection of at least one capacitor and at least one inductor, said series connection being connected in parallel with an inductor. This produces a short circuit for the second frequency.
In another preferred embodiment, the resonator comprises a parallel connection of at least one capacitor and at least one inductor, said series connection being connected in series with a capacitor. This produces a open connection for the second frequency.
The claims and advantanges will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts.